1. Field of the Invention
The present invention relates generally to an actuator, and more particularly, to a compact linear actuator.
2. Description of the Related Art
It has become common prior art that a device based on linear transmission stroke, which is hereinafter referred to as “linear actuator”, is applied to the massage chair, electric chair, electric sickbed, treadmill, collapsible bed, furniture, and lifting mechanism for position adjustment. At least one micro switch is needed to function as controlling the back and forth paths of the linear stroke and the micro switches are mounted to the start and end points of the linear stroke separately. When the linear actuator is moved along the forth path of the linear stroke and touches the micro switch of the end point, the transmission bar is restrictedly no longer moved along the forth path. Relatively, if the linear actuator touches the micro switch located at the start point while moved along the back path, the transmission bar is restrictedly no longer moved along the back path. In this way, a linear reciprocating motion between two points is available, e.g. Taiwan Patent No. M247738.
Referring to Taiwan Patent No. M369950 disclosing a pushrod, where the micro switches are located are different from those of the aforesaid patent. In this patent, the pushrod is composed of a motor, a movable unit, and a stroke control unit. The motor provides power source. The movable unit includes a rotary shaft and a driven member. The stroke control unit includes a timing gear set and at least one micro switch. In operation, the spindle of the motor drives a transmission gear and the timing gear set to enable the transmission gear to drive the rotary shaft of the movable unit for rotation to allow the driven member to move straight along the axial direction of the rotary shaft; the timing gear set forces the micro switch to control rotation of the spindle of the motor to further limit the maximum distance of movement of the driven member, thus preventing the driven member from movement beyond the maximum distance
In Taiwan Patent No. M369950, the pushrod needs the transmission gear set composed of numerous small gears to be driven to function as linearly moving the driven member and operating the micro switch, so the gearbox is huge. In Taiwan Patent No. M247738, the transmission gear set is though not adopted and the micro switch is though hidden straight inside the dustproof sleeve, but it can still make the dustproof sleeve bigger. Thus, the drawbacks of the linear actuators of the aforesaid patents lie in that the gears are excessive, the installation is complicated, and it is difficult to reduce the size, so further improvement is needed.